Communication apparatus and communication method for controlling channel access operation

ABSTRACT

To provide a communication apparatus which controls channel access operation under a multi user environment, and a communication method.Channel access operation of each STA after an MU mode is finished is controlled through a trigger frame from an AP to prevent collision immediately after the MU mode is finished. Further, the AP sets a smaller CW upon transmission of the trigger frame than a CW of an STA to preferentially transmit the trigger frame and give priority to communication in the MU mode over communication in an SU mode. Further, by the CW of each STA upon switching of the mode being not reset, a transmission waiting period after the MU mode is finished is shortened.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/336,907, filed Mar. 27, 2019, which is based on PCT filingPCT/JP2017/029482, filed Aug. 16, 2017, which claims priority to JP2016-212506 filed Oct. 31, 2016, the entire contents of each areincorporated herein by reference.

TECHNICAL FIELD

The technology disclosed in the present specification relates to acommunication apparatus which controls channel access operation under amulti user environment, and a communication method.

BACKGROUND ART

In a wireless LAN typified by IEEE 802.11, or the like, increase ofcommunication speed can be realized by orthogonal frequency divisionmultiple access (OFDMA) and multi user multi-input multi-output(MU-MIMO) being introduced (see, for example, Patent Literature 1).

Here, in OFDM, which is a multi-carrier scheme in which a plurality ofpieces of data is allocated to frequency subcarriers which are“orthogonal”, that is, which do not interfere with each other, eachsubcarrier on a frequency axis can be converted into a signal on a timeaxis and transmitted by inverse fast Fourier transform (FFT) beingperformed on each subcarrier. OFDMA is a multiple access scheme inwhich, instead of one communication station occupying all subcarriers ofan OFDM signal, subcarrier sets on the frequency axis are allocated to aplurality of communication stations, so that subcarriers are sharedamong the plurality of communication stations.

Further, MIMO is a communication scheme which realizes a spatialmultiplexed stream by a plurality of antenna elements being provided atboth a transmitter side and a receiver side. It can be said that MU-MIMOis a spatial division multiple access scheme in which wireless resourceson a spatial axis are shared among a plurality of users.

Communication using OFDMA or MU-MIMO is called a multi user (MU) mode.In contrast to this, one-to-one communication without multiple access iscalled a single user (SU) mode.

CITATION LIST Patent Literature

-   Patent Literature 1: JP 5437307B

DISCLOSURE OF INVENTION Technical Problem

An object of the technology disclosed in the present specification is toprovide an excellent communication apparatus and communication methodwhich enables preferable control of channel access operation under amulti user environment.

Solution to Problem

The technology disclosed in the present specification has been devisedin light of the problem described above, a first aspect thereof is acommunication apparatus that transmits a frame in which informationregarding a transmission waiting period of another terminal isdescribed.

According to a second aspect of the technology disclosed in the presentspecification, the communication apparatus according to the first aspectis configured to operate as an access point, and describe in the framewhich notifies a subordinate terminal of allowance of multi usertransmission, the information designating a transmission waiting periodof the terminal after the multi user transmission is finished.

According to a third aspect of the technology disclosed in the presentspecification, the communication apparatus according to the secondaspect is configured transmit the frame in which the informationdesignating to each terminal a transmission waiting period longer than atransmission waiting period in a case where the communication apparatusperforms multi user transmission after the multi user transmission isfinished, is described.

According to a fourth aspect of the technology disclosed in the presentspecification, the communication apparatus according to the secondaspect is configured to transmit the frame in which the informationdesignating a transmission waiting period different for each terminal isdescribed.

According to a fifth aspect of the technology disclosed in the presentspecification, the communication apparatus according to the secondaspect is configured to transmit the frame in which the informationdesignating a transmission waiting period in accordance with the numberof times of transmission of the terminal is described.

According to a sixth aspect of the technology disclosed in the presentspecification, the communication apparatus according to the fifth aspectis configured to transmit the frame in which the information designatinga transmission waiting period such that a terminal whose number of timesof transmission is smaller has a shorter transmission waiting periodthan a terminal whose number of times of transmission is larger, isdescribed.

According to a seventh aspect of the technology disclosed in the presentspecification, the communication apparatus according to the fifth aspectis configured to transmit the frame in which the information designatinga shorter transmission waiting period for a terminal which performs dataretransmission than a transmission waiting period of another terminal,is described.

According to an eighth aspect of the technology disclosed in the presentspecification, the communication apparatus according to the secondaspect is configured to transmit the frame in which the informationdesignating a longer transmission waiting period for the terminal whichis allowed to perform multi user transmission, than a remainingtransmission waiting period of a terminal which performs dataretransmission, is described.

According to a ninth aspect of the technology disclosed in the presentspecification, the communication apparatus according to the secondaspect is configured to transmit the frame in which a category favorablefor the multi user transmission and the information designating atransmission waiting period for the terminal after the multi usertransmission is finished, are described.

According to a tenth aspect of the technology disclosed in the presentspecification, the communication apparatus according to the ninth aspectis configured to transmit the frame in which the information designatinga transmission waiting period for the terminal in accordance with thecategory is described.

According to an eleventh aspect of the technology disclosed in thepresent specification, the communication apparatus according to theninth aspect is configured to describe, in the frame in which a categorywith higher priority is designated, the information designating atransmission waiting period shorter than a remaining period of atransmission waiting period set in a case where a category with lowerpriority is designated.

In addition, a twelfth aspect of the technology disclosed in the presentspecification is a communication method including: a step oftransmitting a frame in which information regarding a transmissionwaiting period of another terminal is described.

In addition, a thirteenth aspect of the technology disclosed in thepresent specification is a communication apparatus that sets, on thebasis of information regarding a transmission waiting period of thecommunication apparatus described in a received frame, a transmissionwaiting period after communication processing relating to the receivedframe is performed.

In addition, a fourteenth aspect of the technology disclosed in thepresent specification is a communication apparatus that transmits aframe in which information regarding a transmission waiting period ofthe communication apparatus upon next frame transmission is described.

According to a fifteenth aspect of the technology disclosed in thepresent specification, the communication apparatus according to thefourteenth aspect is configured to operate as an access point, anddescribe the information regarding the transmission waiting period ofthe communication apparatus upon the next frame transmission in theframe which notifies a subordinate terminal of allowance of multi usertransmission.

According to a sixteenth aspect of the technology disclosed in thepresent specification, the communication apparatus according to thefifteenth aspect is configured to describe a predetermined value as theinformation in a case where a next frame is not transmitted for a whileafter the frame is transmitted.

According to the seventeenth aspect of the technology disclosed in thepresent specification, the communication apparatus according to thefifteenth aspect is configured to further describe in the frame,information regarding a transmission waiting period upon retransmissionof a frame transmitted by the terminal through the multi usertransmission.

According to an eighteenth aspect of the technology disclosed in thepresent specification, the communication apparatus according to thesixteenth aspect is configured to transmit the frame in which a categoryfavorable for multi user transmission and the information regarding atransmission waiting period upon retransmission in accordance with thecategory are described.

In addition, a nineteenth aspect of the technology disclosed in thepresent specification is a communication method including: a step oftransmitting a frame in which information regarding a transmissionwaiting period of an own communication apparatus upon next frametransmission is described.

In addition, a twentieth aspect of the technology disclosed in thepresent specification is a communication apparatus that sets, on thebasis of information regarding a transmission waiting period upon nextframe transmission by a transmission source of a frame described in thereceived frame, a transmission waiting period of the communicationapparatus after communication processing relating to the received frameis performed.

Advantageous Effects of Invention

According to the technology disclosed in the present specification, itis possible to provide an excellent communication apparatus andcommunication method which enables preferable control of channel accessoperation of subordinate terminals as an access point under a multi userenvironment where a plurality of terminals exists.

According to the technology disclosed in the present specification, itis possible to provide an excellent communication apparatus andcommunication method which enables preferable control of channel accessoperation of an own terminal under a multi user environment where aplurality of terminals exists.

Note that the effects described in the present specification are merelyexamples, and effects of the present invention are not limited to these.Further, there is also a case where the present invention furtherprovides additional effects other than the above-described effects.

Other objects, features and advantages of the technology disclosed inthe present specification will become more clear from the detaileddescription based on an embodiment which will be described later and theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a communication sequence example in thecase where a mode is switched in a wireless LAN network.

FIG. 2 is a diagram illustrating a communication sequence example in thecase where a mode is switched in a wireless LAN network.

FIG. 3 is a diagram illustrating a communication sequence example in thecase where a mode is switched in a wireless LAN network.

FIG. 4 is a diagram illustrating a configuration example of a wirelessLAN system.

FIG. 5 is a diagram illustrating a configuration example of acommunication apparatus 500.

FIG. 6 is a flowchart illustrating operation procedure within thewireless LAN system.

FIG. 7 is a diagram illustrating a configuration example of a triggerframe.

FIG. 8 is a diagram illustrating a communication sequence example (CWsetting by the number of times of transmission) in which a parametervalue of CW of each STA is set at the discretion of an AP.

FIG. 9 is a diagram illustrating a communication sequence example (CWsetting by retransmission) in which the parameter value of the CW ofeach STA is set at the discretion of the AP.

FIG. 10 is a diagram illustrating priority of an AC level.

FIG. 11 is a diagram illustrating a communication sequence example (CWsetting in accordance with the AC level) in which the parameter value ofthe CW of each STA is set at the discretion of the AP.

FIG. 12 is a flowchart illustrating processing procedure in the casewhere the AP transmits the trigger frame.

FIG. 13 is a diagram illustrating a configuration example of the triggerframe.

FIG. 14 is a diagram illustrating a communication sequence example inwhich the parameter value of the CW of each STA is set at the discretionof the STA.

MODE(S) FOR CARRYING OUT THE INVENTION

An embodiment of the technology disclosed in the present specificationwill be described below with reference to the drawings.

In IEEE 802.11 which is one of representative standards of a wirelessLAN, as a mechanism for each terminal to autonomously acquire atransmission opportunity, carrier sense multiple access/collisionavoidance (CSMA/CA) is specified. Specifically, a terminal waits beforetransmission (performs back off) for a random period. Further, in thecase where the terminal observes (performs carrier sense) a surroundingradio wave environment during back off and detects a radio wave havingpower equal to or greater than a certain detection threshold, theterminal stops the back off and suppresses transmission of packets. Bythis mechanism of back off and carrier sense, the terminals avoidcollision of packets while acquiring transmission opportunities in anautonomous and distributed manner.

Normally, in the case where a mode is switched from an MU mode to an SUmode in a wireless LAN, a setting value for determining a transmissionwaiting period such as a contention window (CW) and back off (BO) isreset. In such a case, because a terminal station (STA) cannot restarttransmission immediately after the mode is switched, it is concernedthat utilization efficiency of a transmission path may degrade. Further,as a result of the setting value being reset, because the respectiveSTAs start transmission toward an access point (AP) at the same time,there is a possibility that collision may occur.

FIG. 1 to FIG. 3 illustrate communication sequence examples in the casewhere a mode is switched in the wireless LAN network. However, eachhorizontal axis in the drawings indicates a time axis, each rectangleindicates a frame transmitted from a corresponding communicationapparatus at time corresponding to a position on the horizontal axis,and a parallelogram indicates a transmission waiting period. Further, anarrow extending in a vertical direction from a frame indicates adirection of transmission of the frame (an upward arrow indicates anuplink, and a downward arrow indicates a downlink).

In the example illustrated in each drawing, a network configuration isassumed where two terminal stations STA 1 and STA 2 performcommunication operation under control of the access point (AP), and itis assumed that each STA has an uplink MU function, and the mode isswitched to the MU mode in response to a trigger frame (Trigger) fromthe AP.

Further, in each drawing, the AP, the STA 1 and the STA 2 respectivelyset back off prior to frame transmission and can acquire transmissionopportunities while an interference signal is not detected during a backoff period, that is, during a CW. Typically, the CW is calculated bymultiplying a random value by slot time which is approximately severalmicro seconds. Further, while the CW is reset in the case where packetsare successfully transmitted or in the case where a communication modeis switched, if another packet transmission is started while the backoff is set, the back off is interrupted, and the back off is restartedfrom the remaining period after transmission is finished. Also in theexamples illustrated in FIG. 1 to FIG. 3 , it is assumed that the AP andeach STA randomly set the CW and reset the CW upon switching of themode.

In the example illustrated in FIG. 1 , while the STA 1 sets the backoff, the AP transmits a trigger frame in a format which can be receivedby a plurality of STAs, to subordinate STA 1 and STA 2. The triggerframe described here is a frame for notifying the STA 1 and the STA 2 oftransmission allowance of an uplink data frame, and gives an instructionof an accurate timing for starting transmission and an accurate durationof the frame.

The STA 1 detects a signal from the AP and interrupts the back off.Then, the STA 1 and the STA 2 enter the MU mode in response to allowanceof uplink transmission through the trigger frame, start transmission ofuplink data frames (UL MU PLCP protocol data unit (PPDU)) to the AP atthe same time and complete the transmission at the same time inaccordance with the instruction of the frame. Then, the AP transmits amulti STA block ack (M-BA) frame in a format which can be received byboth the STA 1 and the STA 2, and makes a notification of a receptionresult of the data frame transmitted from each of the STA 1 and the STA2.

After the STA 1 and the STA 2 receive the M-BA from the AP, the STA 1and the STA 2 return to the SU mode. Then, while the STA whose dataframe is successfully received at the AP can prepare for transmission ofnext new data, the STA whose data frame fails to be received preparesfor retransmission of the data. In the example illustrated in FIG. 1 ,the AP fails in reception of the data frame transmitted from the STA 1,and the AP transmits M-BA only to the STA 2.

While the STA 1 prepares for transmitting a retransmission data frameafter the MU mode is finished, the above-described interrupted back offis not restarted from the remaining period, but performed again from thebeginning by the CW being reset upon returning to the SU mode.Therefore, a longer waiting period is set for the STA 1 until the STA 1acquires a retransmission opportunity of the data frame (UL SU PPDU) bythe mode being switched to the MU mode in the middle of the back off.

Further, in the example illustrated in FIG. 2 , the mode of the STA 1and the STA 2 for which uplink transmission is allowed through thetrigger frame is switched to the MU mode by the AP transmitting thetrigger frame for uplink (as described above).

Then, the STA 1 and the STA 2 start transmission of the uplink dataframes (UL MU PPDU) at the same time and complete the transmission atthe same time in accordance with the instruction of the trigger frame,and, in response to this, the AP transmits an M-BA frame and makes anotification of a reception result of the data frame transmitted fromeach of the STA 1 and the STA 2. Here, because the AP fails in receptionof the both data frames transmitted from the STA 1 and the STA 2, theSTA 1 and the STA 2 respectively prepare for transmission ofretransmission data frames.

Thereafter, if the mode returns from the MU mode to the SU mode, the STA1 and the STA 2 respectively reset CWs and try to retransmit data (UL SUPPDU) to the AP. In the example illustrated in FIG. 2 , the STA 1 andthe STA 2 set the CWs at CWmin (a minimum value of the CW) at the sametime. Therefore, there is a problem that a possibility of occurrence ofcollision increases.

Further, in the example illustrated in FIG. 3 , while both the AP andthe STA 2 set the back off, the AP finishes the CW first, and therebyacquires a transmission opportunity, and transmits a trigger frame whichmakes a notification of transmission allowance of an uplink data frameto the STA 1 and the STA 2.

The STA 1 and the STA 2 enter the MU mode in response to this triggerframe, start transmission of uplink data frames (UL MU PPDU) at the sametime and complete the transmission at the same time, and, in response tothis, the AP transmits an M-BA frame and makes a notification of areception result of the data frame transmitted from each of the STA 1and the STA 2. It is assumed here that the data frames transmitted fromthe STA 1 and the STA 2 are both received at the AP.

Thereafter, the AP sets the back off to transmit the second triggerframe. Further, the STA 2 sets the back off to transmit a data frame (ULSU PPDU) to the AP in the SU mode. Here, because a back off counter ofthe STA 2 expires earlier than that of the AP, uplink single usertransmission (UL SU PPDU) by the STA 2 is started, and the AP cannottransmit the second trigger frame immediately after the first uplinkmultiplex communication.

In short, in the example illustrated in FIG. 3 , while the AP tries toperform uplink multiplex communication twice in a row, because thecommunication is interrupted by single user transmission by thesubordinate STA 2, the AP cannot continuously start the second uplinkmultiplex communication. As a result, there is a problem that systemthroughput becomes lower than in the case where uplink multiplexcommunication is continuously performed.

Therefore, the present specification discloses a technology for solvingthe problems as illustrated in FIG. 1 to FIG. 3 by controlling channelaccess operation of each STA after uplink multi user communication isfinished. The technology disclosed in the present specification isrealized with two methods (1) and (2) described below.

-   -   (1) An access control parameter (such as a CW and BO) after the        MU mode of each STA which is a transmission destination is        finished is described in the trigger frame to be transmitted        from the AP side. In response to this, each STA sets a parameter        in accordance with the description of the trigger frame after        the MU mode is finished.    -   (2) Access control parameters of the AP itself and the STA upon        retransmission are described in the trigger frame to be        transmitted from the AP side.

Among the above methods, in the method of (1), the AP appropriately setsthe access control parameter after the MU is finished, which isaddressed to each STA, in accordance with a status. For example, by theaccess control parameter being designated in accordance with priorityamong the STAs, it is possible to shorten a waiting period after the MUmode is finished for the STA with higher priority, so that it ispossible to improve overall system throughput. Further, by the accesscontrol parameters of the respective STAs after the MU mode is finishedbeing set at different values, it is possible to avoid collision. Stillfurther, by each STA restarting back off without resetting a value ofthe access control parameter such as a CW and BO in the case where themode is switched (in the case where the mode returns to the SU mode),each STA can acquire a channel access right immediately without thewaiting period becoming long.

The AP can set the access control parameter for each STA in accordancewith a status of data transmission of each subordinate STA. For example,the AP may set the access control parameter for each STA so that therespective STAs have equal transmission opportunities.

Alternatively, the AP may set the access control parameters of thesubordinate STAs in cooperation with the adjacent BSS. For example, theAP may set the access control parameter of each STA so that an STA whoseinterference wave has less affect on the adjacent BSS can preferentiallyacquire a transmission opportunity.

Further, in the method of the above-described (2), each STA sets aparameter of the STA at the discretion of the STA in response to accesscontrol information of the AP. Further, the STA which performsretransmission after the MU mode is finished sets the parameter of theSTA in accordance with the access control parameter of the STA uponretransmission which is described by the AP in the trigger frame.

FIG. 4 schematically illustrates a configuration example of a wirelessLAN system to which the technology disclosed in the presentspecification can be applied. The illustrated wireless LAN systemincludes one AP and a plurality of STAs among which connection isestablished, and it is assumed that the STA 1, the STA 2, the STA 3, . .. are all under the AP (or belong to a basic service set (BSS) of theAP). The AP and each STA have an OFDMA or MU-MIMO function, and are,so-called, communication apparatuses which can perform communication inthe MU mode.

FIG. 5 illustrates a functional configuration example of thecommunication apparatus 500 which performs communication operation asthe AP or the STA in the wireless LAN system as illustrated in FIG. 4 .It should be understood that a basic configuration of the AP is similarto that of the STA.

The communication apparatus 500 includes a data processing unit 501, acontrol unit 502, a communication unit 503 and a power supply unit 504.Further, the communication unit 501 further includes amodulating/demodulating unit 511, a spatial signal processing unit 512,a channel estimating unit 513, a wireless interface (IF) unit 514, anamplifier unit 515 and an antenna 516. However, one set of the wirelessinterface unit 514, the amplifier unit 515 and the antenna 516 mayconstitute one transmission/reception branch, and two or moretransmission/reception branches may constitute the communication unit501. Further, there is also a case where functions of the amplifier unit515 are incorporated into the wireless interface unit 514.

Upon transmission during which data is input from a protocol upper layer(not illustrated), the data processing unit 501 generates a packet forwireless transmission from the data, performs processing such asaddition of a header for media access control (MAC) and addition of anerror detecting code, and provides the processed data to themodulating/demodulating unit 511. Further, upon reception during whichthere is input from the modulating/demodulating unit 511, the dataprocessing unit 501 performs analysis of MAC Header, detection of apacket error, re-order processing, or the like, and provides theprocessed data to a protocol upper layer of the data processing unit201.

The control unit 502 transfers information among respective units withinthe communication apparatus 500. Further, the control unit 502 performssetting of parameters at the modulating/demodulating unit 511 and thespatial signal processing unit 512, and scheduling of packets at thedata processing unit 501. Still further, the control unit 502 performssetting of parameters of the wireless interface unit 514 and theamplifier unit 515, and transmission power control.

In the case where the communication apparatus 500 operates as the AP,the control unit 502 controls switching of the communication mode(shifting to the MU mode) within the own BSS. Further, in the presentembodiment, the control unit 502 controls each unit so as to transmitthe trigger frame in which an appropriate parameter is described to thesubordinate STAs upon switching to the MU mode. Particularly, in thepresent embodiment, the control unit 502 causes an access controlparameter (such as a parameter for determining a transmission waitingperiod such as a CW and BO and a parameter regarding transmissionpriority, or the like,) after the MU mode of each STA which is atransmission destination is finished to be described or causes an accesscontrol parameter of the AP itself and the STA upon retransmission to bedescribed.

Further, in the case where the communication apparatus 500 operates asthe STA, the control unit 502 controls each unit to perform uplinkmultiplex communication with other subordinate STAs of the AP inaccordance with content described in the trigger frame received from theAP. Particularly, in the present embodiment, the control unit 502 sets atransmission waiting period (a CW and BO) after the MU mode is finishedin accordance with the access control parameter described in the triggerframe, sets a different value from that of other subordinate STAs orsets a parameter such as a CW and BO upon data retransmission at thediscretion of the control unit 502 on the basis of the content describedin the trigger frame.

Upon transmission, the modulating/demodulating unit 511 performsprocessing of encoding, interleaving and modulation on input data fromthe data processing unit 501 on the basis of a coding and modulationscheme set by the control unit 501, generates a data symbol stream andprovides the data symbol stream to the spatial signal processing unit512. Further, upon reception, the modulating/demodulating unit 511performs processing of demodulation, de-interleaving and decoding whichis inverse to the processing upon transmission, on input from thespatial signal processing unit 512 on the basis of the coding andmodulation scheme set by the control unit 501, and provides the data tothe data processing unit 501 or the control unit 502.

Upon transmission, the spatial signal processing unit 512 performssignal processing for space separation on the input from themodulating/demodulating unit 511 as necessary and provides the obtainedone or more transmission symbol streams to respective wireless interfaceunits 514. Meanwhile, upon reception, the spatial signal processing unit512 performs signal processing on the received symbol streams input fromthe respective wireless interface units 514, performs space separationof the streams as necessary and provides the results to themodulating/demodulating unit 511.

The channel estimating unit 513 calculates complex channel gaininformation of a propagation path from a preamble portion and a trainingsignal portion among input signals from the respective wirelessinterface units 514. Then, the calculated complex channel gaininformation is utilized for demodulation processing at themodulating/demodulating unit 511 and spatial processing at the spatialsignal processing unit 512 via the control unit 502, thereby enablingthe MU mode.

Upon transmission, the wireless interface unit 514 converts input fromthe spatial signal processing unit 512 into an analog signal, performsfiltering and up-conversion to a carrier frequency and sends out thesignal to the antenna 516 or the amplifier unit 515. Meanwhile, uponreception, the wireless interface unit 514 performs processing ofdown-conversion and conversion to a digital signal, which is processinginverse to processing upon transmission, on input (received signal ofthe carrier frequency) from the antenna 516 or the amplifier unit 515,and provides the data to the spatial signal processing unit 512 and thechannel estimating unit 513.

Upon transmission, the amplifier unit 515 amplifies the analog signalinput from the wireless interface unit 514 to predetermined power andsends out the signal to the antenna 516. Further, upon reception, theamplifier unit 515 amplifies low noise of the received signal input fromthe antenna 516 to predetermined power and outputs the signal to thewireless interface unit 514. There is a case where at least one offunctions upon transmission or functions upon reception of the amplifierunit 515 is incorporated into the wireless interface unit 514.

The power supply unit 504 is constituted with a battery power supply ora fixed power supply such as a commercial power supply, and suppliespower for drive to each unit within the communication apparatus 500.

Note that, while the communication apparatus 500 can further includefunctional modules other than the illustrated modules, because thefunctional modules other than the illustrated modules are not directlyrelated to the technology disclosed in the present specification,illustration and description will be omitted here.

In the wireless LAN system, a method for setting a CW of each STA can beroughly divided into two methods of a method in which setting is made inaccordance with a notification from the AP and a method in which settingis made at the discretion of the STA. The same will also apply to amethod for setting a BO. In the following description, description willbe provided using Example 1 which uses the method in which setting ismade at the discretion of the AP and Example 2 which uses the method inwhich setting is made at the discretion of the STA.

Example 1

FIG. 6 illustrates operation procedure within the wireless LAN system ina form of a flowchart, in the case where a CW for each STA is set inaccordance with a notification from the AP.

In the wireless LAN, specifications for randomly accessing a channel areemployed. Therefore, the AP and each subordinate STA compete with eachother to perform transmission within the network (step S601).

Here, the AP has already acquired information of the STAs having an MUfunction at an early stage at which the AP is connected to each STA.Therefore, the AP sets parameters for channel access (such as a CW andBO) to a plurality of STAs having the MU function and creates a triggerframe in which these set parameters for channel access are described(step S602). Then, the AP transmits the above-described trigger frame inwhich the parameters for channel access are described to each STA forwhich uplink data transmission to the AP in the MU mode is allowed afteracquiring a channel access right (step S603).

The mode of each STA which receives the trigger frame is switched to theMU mode, and each STA starts transmission of the uplink data frame (ULMU PPDU) at the same time and completes the transmission at the sametime in accordance with an instruction of the trigger frame (step S604).

In response to this, the AP makes a notification of a reception resultof the data frame transmitted from each STA (step S605). The AP notifieseach STA of this reception result by transmitting an M-BA frame(mentioned above) or transmitting a BA frame (not illustrated) to eachSTA through downlink multiplex transmission or a plurality of times ofsingle user transmission.

Each STA sets a CW value described in the trigger frame received in stepS603 after communication with the AP is completed, that is, after the MUmode is finished (step S606). For example, the STA which receives anotification indicating that the AP fails in reception of the data frametransmitted in the MU mode can shorten a waiting period or avoidcollision with other STAs by performing access control of a channelusing the CW value set in accordance with the description of the triggerframe upon returning to the SU mode.

The above-described method (1) is a method in which the AP sets at leastone parameter value of the CW or the BO of each STA after the MU mode isfinished at the discretion of the AP. The AP describes information to beused for setting a transmission waiting period at the STA side, such asa parameter value of the CW or the BO designated to each STA in thetrigger frame, and transmits the trigger frame to each STA as a cue foruplink multiplex communication.

FIG. 7 illustrates a configuration example of the trigger frameincluding description of the parameter value of the CW or the BO to bedesignated to each STA. The trigger frame has a user information (UserInfo) filed for information for each STA (user) other than informationcommon among the STAs which become destinations. In the frameconfiguration example illustrated in FIG. 7 , the parameter values ofthe CW and the BO set for each STA at the discretion of the AP aredescribed in the respectively corresponding User Info fields. Further,in the illustrated example, while the both parameter values of the CWand the BO are included in the respective User Info fields, it is alsopossible to employ a configuration where only one of the parametervalues is included.

There are some possible methods for the AP to determine the parametervalue of the CW or the BO of each STA. For example, examples of themethods include a method in which the CW is set using the number oftimes of transmission of each STA, a method in which the CW is set inaccordance with priority of each STA, a method in which the CW is set inaccordance with an access category (AC), or the like.

The method for the AP to set the CW on the basis of the number of timesof transmission of each STA will be described with reference to thecommunication sequence example illustrated in FIG. 8 . However, in thedrawing, each rectangle indicates a frame, an arrow indicates adirection of transmission (an upward arrow indicates an uplink, and adownward arrow indicates a downlink). Further, a network configurationis assumed where three terminal stations STA 1, STA 2 and STA 3 performcommunication operation under control of the AP, and it is assumed thateach STA has an uplink MU function. Further, a CW value set for the i-thterminal STAi immediately after the n-th multi user transmission isexpressed as CW_i_n. The terminal STAi can calculate a transmissionwaiting period immediately after the n-th multi user transmission bymultiplying CW_i_n by slot time (the same hereinafter).

In the case where the AP acquires a channel access right, in the casewhere the AP performs reception through UL MU from the STA 1 and the STA2, the AP describes the CW values CW_1_1 and CW_2_1 respectively set forthe STA 1 and the STA 2 on the basis of an expected duration of UL MU inthe first trigger frame and transmits the first trigger frame. Notethat, while there is a case where corresponding values of BO Backoff 1_1and Backoff 2_1 are set at the respective STAs, to simplify thedescription, this case will be omitted in the following description. TheAP sets different values as CW_1_1 and CW_2_1 respectively at the STA 1and the STA 2 at the discretion of the AP. Therefore, collision does notoccur by the STA 1 and the STA 2 transmitting frames at the same timeafter UL MU is finished.

The STA 1 and the STA 2 start transmission of uplink data frames (UL MUPPDU) at the same time and complete the transmission at the same time inaccordance with an instruction of the trigger frame. Then, the APtransmits an M-BA frame to make a notification of a reception result ofthe data frame transmitted from each of the STA 1 and the STA 2. It isassumed in the illustrated example that the data frames transmitted fromthe STA 1 and the STA 2 are both successfully received at the AP, andthe AP transmits M-BA which makes a notification of the reception resultto the STA 1 and the STA 2.

Further, in the example illustrated in FIG. 8 , it is expected that theAP further performs reception from the STA using the second UL MU.Therefore, both the CW setting values CW_1_1 and CW_2_1 respectively forthe STA 1 and the STA 2 described in the first trigger frame are setgreater than a CW setting value CW_AP_1 for the AP itself. Conditionsfor the CW set for each of the AP, the STA 1 and the STA 2 will bedescribed below.CW_1_1≠CW_2_1CW_1_1,CW_2_1>CW_AP_1

After the first UL MU transmission is finished, the AP and the STA 2have a schedule for transmission within the network, and both start backoff. As described above, the CW value CW_2_1 set by the AP for the STA 2and designated in the first trigger frame is greater than the CW valueCW_AP_1 set for the AP itself. Therefore, after the first UL MUtransmission is finished, there is a high possibility that the APpreferentially acquires a channel access right. Therefore, the AP cancontinuously transmit the second trigger frame, so that it becomes easyto perform reception from the STA in the second UL MU. In this event,the STA 2 interrupts the back off.

Further, while the AP allows uplink data transmission for the STA 1 andthe STA 3 in the second UL MU, because data transmission is not allowedfor the STA 2, the AP describes the CW values CW_1_2 and CW_3_2respectively set for the STA 1 and the STA 3 on the basis of an expectedduration of the second UL MU in the second trigger frame and transmitsthe second trigger frame.

The STA 1 and the STA 3 start transmission of the second uplink dataframes (UL MU PPDU) at the same time and complete the transmission atthe same time in accordance with an instruction of the second triggerframe. In this event, the AP successfully receives the data frames fromthe STA 1 and the STA 3, and transmits M-BA which makes a notificationof reception results to the STA 1 and the STA 3.

After the second UL MU transmission is finished, because the STA 2 stillhas a schedule of transmission, the STA 2 restarts back off which isinterrupted by transmission of the second trigger frame from the AP.Here, the CW of the STA 2 is not reset upon returning to the SU mode.Therefore, because the STA 2 restarts back off with the remaining valueof CW_2_1 (that is, CW_2_1−CW_AP_1) after the second UL MU transmissionis finished, the STA 2 can immediately acquire a channel access right,so that the STA 2 can easily perform transmission in the SU mode. Then,in the case where the AP successfully receives the data frame (UL SUPPDU) from the STA 2, the AP transmits S-BA which makes a notificationof the reception result to the STA 2.

Meanwhile, in the case where the STA 1 acquires more UL MU transmissionrights than STA 2 and the STA 3 at a time point at which the first UL MUmode is finished, by transmission priority of the STA 1 being lowered,fairness of the system is improved. For example, by CW_1_2 of the STA 1being made greater than CW_3_2 of the STA 3 in the second trigger framein accordance with the following conditions, it is possible to lowertransmission priority of the STA 1 (or increase transmission priority ofthe STA 3) by shortening a transmission waiting period of the STA 3 at atime point at which the second UL MU mode is finished. Further, byCW_1_2 of the STA 1 being set greater than a CW value (CW_2_1−CW_AP_1)corresponding to the remaining transmission waiting period of the STA 2,it is possible to lower transmission priority of the STA 1 (or increasetransmission priority of the STA 2) by making the transmission waitingperiod of the STA 2 which restarts back off shorter than thetransmission waiting period of the STA 1 at a time point at which thesecond UL MU mode is finished.CW_1_2>CW_3_2CW_1_2>CW_2_1−CW_AP_1

By the above-described setting conditions of the CW value of each STA,an effect is provided that it is possible to secure transmissionpriority of the STA 2 and the STA 3 which have a smaller number of timesof transmission by postponing transmission start time of the STA 1 afterthe second MU mode is finished.

Subsequently, a method for the AP to set a CW through retransmissionwill be described with reference to the communication sequence diagramillustrated in FIG. 9 . However, in the drawing, each rectangleindicates a frame, and an arrow indicates a direction of transmission(an upward arrow indicates an uplink, and a downward arrow indicates adownlink). Further, a network configuration is assumed where threeterminal stations STA 1, STA 2 and STA 3 perform communication operationunder control of the AP, and it is assumed that each STA has an uplinkMU function.

If the AP acquires a channel access right, in the case where the APperforms reception through UL MU from the STA 1 and the STA 2, the APdescribes the CW values CW_1_1 and CW_2_1 respectively set at the STA 1and the STA 2 in the first trigger frame and transmits the first triggerframe.

Here, in the case where it is expected that the AP further performsreception from the STA through the second UL MU, in a similar manner tothe communication sequence example illustrated in FIG. 8 , both the CWsetting values CW_1_1 and CW_2_1 for the respective STA 1 and the STA 2described in the first trigger frame may be set greater than the CWsetting value CW_AP_1 of the AP itself.

The STA 1 and the STA 2 start transmission of the first uplink dataframes (UL MU PPDU) at the same time and complete the transmission atthe same time in accordance with an instruction in the trigger frame. Inthis event, while the AP successfully receives the data frame from theSTA 1, the AP fails in reception of the data frame from the STA 2.Therefore, the AP encourages the STA 2 to retransmit the data byexcluding BA addressed to the STA 2 in M-BA which makes a notificationof the reception result.

After the first UL MU transmission is finished, the AP starts back offto further perform reception from the STA through the second UL MU.Further, the STA 2 starts back off to retransmit the data frame whichhas failed to be received at the AP. In the case where the CW valueCW_2_1 set by the AP for the STA 2 and indicated in the first triggerframe is greater than the CW value CW_AP_1 set for the AP itself, the APpreferentially acquires a channel access right and continuouslytransmits the second trigger frame. In this event, the STA 2 interruptsthe back off.

Further, while the AP allows uplink data transmission for the STA 1 andthe STA 3 in the second UL MU, because data transmission is not allowedfor the STA 2, the AP describes the CW values CW_1_2 and CW_3_2respectively set for the STA 1 and the STA 3 on the basis of an expectedduration of the second UL MU in the second trigger frame and transmitsthe second trigger frame.

The STA 1 and the STA 3 start transmission of the second uplink dataframes (UL MU PPDU) at the same time and complete the transmission atthe same time in accordance with an instruction of the second triggerframe. In this event, the AP successfully receives the data frames fromthe STA 1 and the STA 3, and transmits M-BA which makes a notificationof reception results to the STA 1 and the STA 3. Meanwhile, becausetransmission by the STA 2 is not allowed in the second trigger frame,the STA 2 cannot retransmit the data which has failed to be received atthe AP, through the second UL MU.

After the second UL MU transmission is finished, because the STA 2 has aschedule of retransmitting the data to the AP, the STA 2 restarts backoff for data retransmission through the second trigger frametransmission from the AP. Here, retransmission by the STA 2 is made tobe preferentially performed after the second UL MU mode is finished.

For example, by CW_1_2 of the STA 1 being set greater than the CW value(CW_2_1−CW_AP_1) corresponding to the remaining transmission waitingperiod of the STA 2 and CW_3_2 of the STA 3 being set greater than theCW value (CW_2_1−CW_AP_1) corresponding to the remaining transmissionwaiting period of the STA 2 in the second trigger frame in accordancewith the following conditions, it is possible to increase priority ofretransmission by the STA 2 by making the transmission waiting period ofthe STA 2 which restarts back off at a time point at which the second ULMU mode is finished shorter than the transmission waiting periods of theSTA 1 and the STA 3.CW_1_2>CW_2_1−CW_AP_1CW_3_2>CW_2_1−CW_AP_1

According to the above-described setting conditions of the CW value ofeach STA, by the transmission waiting periods of the STA 1 and the STA 3being set longer, even if at least one of the STA 1 or the STA 3 startsback off after the second MU mode is finished, an effect is providedthat the STA 2 can preferentially perform retransmission.

That is, because the STA 2 restarts back off with the remaining value ofCW_2_1 (CW_2_1−CW_AP_1) without resetting the CW value upon returning tothe SU mode, the STA 2 can acquire a channel access right immediately,so that the STA 2 can easily perform data retransmission. Then, if theAP successfully receives the data frame (UL SU PPDU) from the STA 2, theAP transmits S-BA which makes a notification of a reception result tothe STA 2.

Subsequently, a method for the AP to set the CW in accordance with an AClevel will be described.

For example, in enhanced distributed channel access (EDCA) specified inIEEE 802.11e standards which are directed to providing a quality ofservice (QoS) function, a mechanism is employed where packets areclassified into four ACs, stored in respective queues and transmitted inaccordance with priority for each AC. Four ACs described here are AC_VO(Voice), AC_VI (Video), AC_BE (Best Effort) and AC_BK (Background), andpriority of each AC is as indicated in FIG. 10 .

To maximize the effect of MU, it is considered desirable that the APallows data transmission by the STAs having the same AC at the same timein the UL MU mode. To realize this, a favorable AC level is described ina Common Info field (see FIG. 7 ) of the trigger frame transmitted fromthe AP, and, in response to this, a signal which best meets the AC levelis transmitted at the STA side which is allowed to perform transmission.The STA transmits a packet having priority which is the same as orhigher than the AC level designated in the trigger frame in the UL MUmode in the case where transmission is allowed in the trigger frame.

In this method, the AP sets CWs to a plurality of STAs in accordancewith the respective AC levels. A method to set a CW in accordance withthe AC level will be described with reference to the communicationsequence diagram illustrated in FIG. 11 . However, in the drawing, eachrectangle indicates a frame, and an arrow indicates a direction oftransmission (an upward arrow indicates an uplink, and a downward arrowindicates a downlink). Further, a network configuration is assumed wherethree terminal stations STA 1, STA 2 and STA 3 perform communicationoperation under control of the AP, and it is assumed that each STA hasan uplink MU function.

In the case where the AP acquires a channel access right, the APdescribes a favorable AC level in the Common Info field of the firsttrigger frame, describes the CW values set on the basis of priority ofthe AC (se FIG. 10 ) for the STA 1 and the STA 2 which are allowed toperform transmission in the respective User Info fields, and performstransmission. Basically, a smaller CW value is set for the AC withhigher priority. Here, because the AC levels of the STA 1 and the STA 2are lower, transmission is performed while greater CW values CW_1_1 andCW_2_1 are set and described in the first trigger frame.

The STA 1 and the STA 2 start transmission of packets having prioritywhich is the same as or higher than the AC level designated in thetrigger frame at the same time and complete the transmission at the sametime. In this event, the AP successfully receives data frames from theSTA 1 and the STA 2 and transmits M-BA which makes a notification ofreception results to the STA 1 and the STA 2.

After the first UL MU transmission is finished, the AP starts back offto further perform reception from the STA through the second UL MU, andif the AP acquires a channel access right, the AP continuously transmitsthe second trigger frame. Here, the AP sets a higher AC level than thatin the previous MU mode, sets smaller CW values CW_1_2 and CW_3_2 forthe STA 1 and the STA 3 for which transmission is allowed in accordancewith the AC levels, and transmits the second trigger frame in whichthese kinds of information are described. For example, the AP setsCW_1_2 of the STA 1 smaller than the CW values (CW_1_1−CW_AP_1 andCW_2_1−CW_AP_1) corresponding to remaining periods of the transmissionwaiting periods respectively set by the STA 1 and the STA 2 inaccordance with the first trigger frame with low priority, and setsCW_3_2 of the STA 3 smaller than the CW values (CW_1_1−CW_AP_1 andCW_2_1−CW_AP_1) corresponding to the remaining transmission periods in asimilar manner, in the second trigger frame in which the AC level withhigh priority is designated, in accordance with the followingconditions.CW_1_2>CW_1_1−CW_AP_1,CW_2_1−CW_AP_1CW_3_2>CW_1_1−CW_AP_1,CW_2_1−CW_AP_1

Further, because the STA 1 has already been able to perform second datatransmission, in terms of fairness of the system (mentioned above),CW_3_2 is set at a smaller value than CW_1_2 to lower priority of theSTA 1 in accordance with the number of times of transmission.CW_3_2<CW_1_2

The STA 1 and the STA 3 start transmission of the second uplink dataframes (UL MU PPDU) at the same time and complete the transmission atthe same time in accordance with an instruction of the second triggerframe. In this event, the AP successfully receives the data frames fromthe STA 1 and the STA 3, and transmits M-BA which makes a notificationof reception results to the STA 1 and the STA 3.

After the second UL MU transmission is finished, because the STA 3 stillhas a schedule of transmission, the STA 3 starts back off using a CWsetting value (CW_3_2) described in the second trigger frame. Asmentioned above, CW_3_2 is smaller than any of the CW values(CW_1_1−CW_AP_1 and CW_2_1−CW_AP_1) corresponding to the remainingperiods of the back off periods set by the STA 1 and the STA 2 after thefirst UL MU transmission, and is smaller than CW_1_2 designated in thesecond trigger frame for the STA 1. Therefore, the STA 3 which has ahigh AC level and which has performed UL MU transmission easily acquiresa transmission opportunity.

Then, the STA 3 transmits a data frame (UL SU PPDU) to the AP in the SUmode in the case where the STA 3 can acquire a channel access right.Then, in the case where the AP successfully receives the data frame fromthe STA 3, the AP transmits S-BA which makes a notification of areception result to the STA 3.

While the three methods in which the CW is set at the discretion of theAP have been described above, in actual operation, it is sufficient ifthe AP comprehensively performs judgement to control a value of the CWor the BO of each STA using these three methods at the same time.

FIG. 12 illustrates processing procedure in a form of a flowchart, forthe AP to transmit the trigger frame in the present example. Theillustrated processing procedure is basically performed mainly by thecontrol unit 502 in the case where the communication apparatus 500illustrated in FIG. 5 operates as the AP.

The AP first determines a transmission destination of the trigger frame,that is, an STA which is allowed to perform uplink data transmission tothe AP itself in the next MU mode (step S1201).

Then, the AP sets the number of times of transmission in the UL MU mode.In this event, in the case where it is expected that the AP continuouslyperforms UL MU communication, the AP sets a CW value greater than the CWvalue of the AP itself for each STA (step S1202).

Then, the AP increments by one the number of times of transmission inthe UL MU mode of each STA which is allowed to perform transmission(step S1203).

Then, the AP sets a CW value for each STA which is allowed to performtransmission in step S1201 in accordance with the number of times oftransmission (step S1204). Specifically, the AP sets a smaller CW valuefor the STA whose number of times of transmission is smaller (mentionedabove).

Further, the AP adjusts the CW value set for each STA in accordance withthe AC level described in the trigger frame (step S1205).

Then, the AP checks whether each STA which becomes a transmissiondestination of the trigger frame exists in a retransmission list (stepS1206). Then, in the case where an STA which is a transmissiondestination exists in the retransmission list (step S1206: Yes), the APreduces the CW value of the STA (step S1207). Alternatively, in stepS1207, processing may be replaced with processing of increasing a CWvalue of an STA which does not exist in the retransmission list (thatis, which does not perform retransmission).

Then, the AP describes the CW values of the respective STAs set asdescribed above in the respective corresponding User Info fields in thetrigger frame (step S1208) and finishes the present processing routine.

Example 2

In the method in which the CW or the BO is set at the discretion of theSTA, upon setting other than upon retransmission, instead of the settingvalue of the CW or the BO of each STA being designated from the AP, theSTA sets a parameter value of the CW, the BO, or the like, on the basisof the information described in the trigger frame received from the APin addition to at the discretion of the STA.

FIG. 13 illustrates a configuration example of the trigger frame used inthis method. In the illustrated trigger frame, a field called a ControlParameters field is added. The Control Parameters field includes TriggerCW Parameter, Backoff Parameter, and Retry Parameter.

Among these, Trigger CW Parameter and Backoff Parameter respectivelydescribe values of the CW and the BO in the case where the AP transmitsthe next trigger frame. The subordinate STA which receives the triggerframe, for example, sets a CW value which is greater than the CW valueof the AP at the discretion of the STA so as to prevent interruption ina trigger frame which the AP tries to transmit next.

Further, Retry Parameter is a CW setting value for only the STA whichperforms retransmission, and controls the CW value in the case where theSTA which receives the trigger frame performs retransmission. The APsets Retry Parameter in accordance with the priority. For example, theAP determines the CW value upon retransmission by the STA in accordancewith the AC level. By smaller Retry Parameter being described in atrigger frame in which an AC level with higher priority is described,the STA whose priority of the AC is higher can perform transmissionfirst in the case where a plurality of STAs performs retransmission.

Note that, in the case where the AP does not perform UL MU for a whileafter the AP finishes UL MU communication of this time, the subordinateSTA may be notified by, for example, a certain value (for example, 0)being described in Trigger CW Parameter and Backoff Parameter. The STAwhich receives such a trigger frame only has to perform back off using apredetermined method.

In the case where it is expected that the AP further performs receptionfrom the STA through the second UL MU, the AP can make a notification ofa waiting period until the AP transmits the next trigger frame throughdescription of Trigger CW Parameter or Backoff Parameter within thetrigger frame. In response to this, the STA side sets a longer waitingperiod for the STA than the waiting period for the AP notified in thetrigger frame. By this means, the STA cannot interrupt the APimmediately after the UL MU communication is finished, so that the APcan easily and continuously start UL MU communication.

A method for the STA to receive the trigger frame illustrated in FIG. 13from the AP and set the CW at the discretion of the STA will bedescribed with reference to the communication sequence diagramillustrated in FIG. 14 . However, in the drawing, each rectangleindicates a frame, and an arrow indicates a direction of transmission(an upward arrow indicates an uplink, and a downward arrow indicates adownlink). Further, a network configuration is assumed where threeterminal stations STA 1, STA 2 and STA 3 perform communication operationunder control of the AP, and it is assumed that each STA has an uplinkMU function.

In the case where the AP acquires a channel access right, the APtransmits the first trigger frame which allows transmission to the STA 1and the STA 2. In this event, in the case where it is expected that theAP further performs reception from the STA through UL MU, the APdescribes Trigger CW parameter or Backoff Parameter within a ControlParameter field within the trigger frame to notify each subordinate STAof a waiting period (CW_AP_1) until the AP itself transmits the nexttrigger frame after the first UL MU communication.

Further, the AP can control the CW value in the case where the STA whichreceives the trigger frame performs retransmission by describing a CWsetting value only for the STA which performs retransmission in RetryParameter within the Control Parameter field within the trigger frame.

The STA 1 and the STA 2 start transmission of the first uplink dataframes (UL MU PPDU) at the same time and complete the transmission atthe same time in accordance with an instruction of the first triggerframe. In this event, while the AP successfully receives the data framefrom the STA 1, the AP fails in reception of the data frame from the STA2. Therefore, the AP encourages the STA 2 to retransmit the data byexcluding BA addressed to the STA 2 in M-BA which makes a notificationof the reception result.

After the first UL MU transmission is finished, the AP starts back offto further perform reception from the STA through the second UL MU.Further, the STA 2 starts back off to retransmit the data frame whichhas failed to be received at the AP.

In this event, the STA 2 sets the CW value of the STA 2 greater than theCW value of the AP (CW_AP_1) notified through Trigger CW Parameter orBackoff Parameter within the first trigger frame at the discretion ofthe STA 2 itself. Therefore, the AP can preferentially acquire a channelaccess right, and the AP continuously transmits the second triggerframe.

Alternatively, in the case where the CW value only for retransmission isdescribed in the Retry Parameter field of the first trigger frame, theSTA 2 sets a transmission waiting period based on this CW value andstarts back off for retransmission of the data frame which has failed tobe received at the AP in the first UL MU transmission. In the case whereit is expected that UL MU transmission is continuously performed, the APdescribes a CW value greater than the CW value (CW_AP_1) set for the APin the Retry Parameter field. Therefore, if the STA 2 sets thetransmission waiting period for data retransmission in accordance withdescription in the Retry Parameter field, the AP can preferentiallyacquire a channel access right, and continuously transmits the secondtrigger frame.

Note that the AP can determine a CW setting value only forretransmission in accordance with the AC level. For example, in thefirst trigger frame, the AC level with higher priority is described, anda smaller CW value is described in Retry Parameter as priority ishigher, while, in the second trigger frame, an AC level with lowerpriority is described, and a greater CW value is described in RetryParameter as priority is lower. By this means, the STA 2 which performsretransmission of data which has failed to be received at the AP in thefirst UL MU transmission can retransmit the data with a higher AC levelfirst by a shorter transmission waiting period being set for the STA 2than the STA which has failed in the second UL MU transmission.

Referring to FIG. 14 again, description will be continued. While the APallows uplink data transmission to the STA 1 and the STA 3 in the secondtrigger frame, the AP does not allow data transmission to the STA 2.

The STA 1 and the STA 3 start transmission of the second uplink dataframes (UL MU PPDU) at the same time and complete the transmission atthe same time in accordance with an instruction of the second triggerframe. In this event, the AP successfully receives the data frames fromthe STA 1 and the STA 3, and transmits M-BA which makes a notificationof reception results to the STA 1 and the STA 3. Meanwhile, the STA 2cannot retransmit the data which has failed to be received at the AP,through the second UL MU.

After the second UL MU transmission is finished, because the STA 2 has aschedule of retransmitting the data to the AP, the STA 2 restarts backoff. Here, because the STA 2 restarts back off with the remaining valueof CW without resetting the CW setting value upon returning to the SUmode, the STA 2 can acquire a channel access right immediately, so thatthe STA 2 can easily perform data retransmission. Then, if the APsuccessfully receives the data frame (UL SU PPDU) from the STA 2, the APtransmits S-BA which makes a notification of a reception result to theSTA 2.

Note that this method can be also realized by the AP informing insidethe BSS of the values of the CW and the BO in the case where the APtransmits the next trigger frame by describing the values in a beaconframe instead of in the trigger frame.

The following effects can be expected by the technology disclosed in thepresent specification being applied to the wireless LAN systemsupporting the MU mode.

-   -   (1) It is possible to prevent collision immediately after the MU        mode is finished by channel access operation of each STA after        the MU mode is finished being controlled through the trigger        frame to be transmitted from the AP.    -   (2) As a result of the CW in the case where the AP transmits the        trigger frame being set smaller than the CW of the STA or by the        CW of the STA after the MU mode is finished being set greater,        it is possible to cause communication in the MU mode to be        preferentially performed than in the SU mode by enabling the        trigger frame to be preferentially transmitted from the AP.    -   (3) Because the CW of each STA is not reset in the case where        the mode is switched from the MU mode to the SU mode, the STA        can shorten a waiting period until transmission since the MU        mode has been finished, so that communication efficiency is        improved.    -   (4) By the CW being set in accordance with priority of the STA,        it is possible to improve overall efficiency of the system.

INDUSTRIAL APPLICABILITY

The technology disclosed in the present specification has been describedin detail above with reference to the specific embodiment. However, itwill be obvious to those skilled in the art that modification andreplacement of the embodiment can be made without departing from thescope of the technology disclosed in the present specification.

While, in the present specification, the embodiment to which thetechnology disclosed in the present specification is applied to awireless LAN network to which IEEE 802.11ax standards are applied hasbeen mainly described, gist of the technology disclosed in the presentspecification is not limited to this. The technology disclosed in thepresent specification can be also applied in a similar manner to variouscommunication systems in which uplink multi user transmission isperformed or one or more terminals operate under the control of anaccess point.

In short, the technology disclosed in the present specification has beendescribed in an illustrative form, and the description of the presentspecification should not be interpreted in a limited manner. The claimsshould be taken into account to judge the gist of the technologydisclosed in the present specification.

Additionally, the present technology may also be configured as below.

-   -   (1)        -   A communication apparatus that transmits a frame in which            information regarding a transmission waiting period of            another terminal is described.    -   (2)        -   The communication apparatus according to (1),        -   in which the communication apparatus operates as an access            point, and describes in the frame which notifies a            subordinate terminal of allowance of multi user            transmission, the information designating a transmission            waiting period of the terminal after the multi user            transmission is finished.    -   (3)        -   The communication apparatus according to (2),        -   in which the communication apparatus transmits the frame in            which the information designating to each terminal a            transmission waiting period longer than a transmission            waiting period in a case where the communication apparatus            performs multi user transmission after the multi user            transmission is finished, is described.    -   (4)        -   The communication apparatus according to any of (2) or (3),        -   in which the communication apparatus transmits the frame in            which the information designating a transmission waiting            period different for each terminal is described.    -   (5)        -   The communication apparatus according to any of (2) to (4),        -   in which the communication apparatus transmits the frame in            which the information designating a transmission waiting            period in accordance with the number of times of            transmission of the terminal is described.    -   (6)        -   The communication apparatus according to (5),        -   in which the communication apparatus transmits the frame in            which the information designating a transmission waiting            period such that a terminal whose number of times of            transmission is smaller has a shorter transmission waiting            period than a terminal whose number of times of transmission            is larger, is described.    -   (7)        -   The communication apparatus according to (5),        -   in which the communication apparatus transmits the frame in            which the information designating a shorter transmission            waiting period for a terminal which performs data            retransmission than a transmission waiting period of another            terminal, is described.    -   (8)        -   The communication apparatus according to any of (2) to (7),        -   in which the communication apparatus transmits the frame in            which the information designating a longer transmission            waiting period for the terminal which is allowed to perform            multi user transmission, than a remaining transmission            waiting period of a terminal which performs data            retransmission, is described.    -   (9)        -   The communication apparatus according to any of (2) to (8),        -   in which the communication apparatus transmits the frame in            which a category favorable for the multi user transmission            and the information designating a transmission waiting            period for the terminal after the multi user transmission is            finished, are described.    -   (10)        -   The communication apparatus according to (9),        -   in which the communication apparatus transmits the frame in            which the information designating a transmission waiting            period for the terminal in accordance with the category is            described.    -   (11)        -   The communication apparatus according to any of (9) or (10),        -   in which, in the frame in which a category with higher            priority is designated, the information designating a            transmission waiting period shorter than a remaining period            of a transmission waiting period set in a case where a            category with lower priority is designated, is described.    -   (12)        -   A communication method including:        -   a step of transmitting a frame in which information            regarding a transmission waiting period of another terminal            is described.    -   (13)        -   A communication apparatus that sets, on the basis of            information regarding a transmission waiting period of the            communication apparatus described in a received frame, a            transmission waiting period after communication processing            relating to the received frame is performed.    -   (14)        -   A communication apparatus that transmits a frame in which            information regarding a transmission waiting period of the            communication apparatus upon next frame transmission is            described.    -   (15)        -   The communication apparatus according to (14),        -   in which the communication apparatus operates as an access            point, and describes the information regarding the            transmission waiting period of the communication apparatus            upon the next frame transmission in the frame which notifies            a subordinate terminal of allowance of multi user            transmission.    -   (16)        -   The communication apparatus according to (15),        -   in which the communication apparatus describes a            predetermined value as the information in a case where a            next frame is not transmitted for a while after the frame is            transmitted.    -   (17)        -   The communication apparatus according to any of (15) or            (16),        -   in which the communication apparatus further describes in            the frame, information regarding a transmission waiting            period upon retransmission of a frame transmitted by the            terminal through the multi user transmission.    -   (18)        -   The communication apparatus according to (17),        -   in which the communication apparatus transmits the frame in            which a category favorable for multi user transmission and            the information regarding a transmission waiting period upon            retransmission in accordance with the category are            described.    -   (19)        -   A communication method including:        -   a step of transmitting a frame in which information            regarding a transmission waiting period of an own            communication apparatus upon next frame transmission is            described.    -   (20)        -   A communication apparatus that sets, on the basis of            information regarding a transmission waiting period upon            next frame transmission by a transmission source of a frame            described in the received frame, a transmission waiting            period of the communication apparatus after communication            processing relating to the received frame is performed.

REFERENCE SIGNS LIST

-   -   500 communication apparatus    -   501 data processing unit    -   502 control unit    -   503 communication unit    -   504 power supply unit    -   511 modulating/demodulating unit    -   512 spatial signal processing unit    -   513 channel estimating unit    -   514 wireless interface unit    -   515 amplifier unit    -   516 antenna

The invention claimed is:
 1. An access point apparatus comprising:circuitry configured to transmit a frame in which information of acategory favorable for uplink multi user transmission and informationregarding a transmission waiting period of a communication apparatusafter the uplink multi user transmission is finished are included, andinclude, in the frame, the information regarding the transmissionwaiting period of the communication apparatus in accordance with thecategory, wherein the category includes AC_VO, AC_VI, AC_BE, or AC_BK,wherein the circuitry is configured to include, in the frame, theinformation regarding the transmission waiting period longer thananother transmission waiting period in a case where the access pointapparatus performs another uplink multi user transmission after theuplink multi user transmission is finished, and wherein the circuitry isconfigured to acquire, based on back off, an opportunity to trigger theuplink multi user transmission, and acquire, based on the othertransmission waiting period, another opportunity to trigger the otheruplink multi user transmission.
 2. The access point apparatus accordingto claim 1, wherein the information regarding the transmission waitingperiod includes information regarding a contention window.
 3. The accesspoint apparatus according to claim 1, wherein the circuitry isconfigured to transmit the frame including the information designating atransmission waiting period which is different for each communicationapparatus.
 4. The access point apparatus according to claim 1, whereinthe circuitry is configured to transmit the frame including theinformation designating the transmission waiting period in accordancewith a number of times of transmission of the communication apparatus.5. The access point apparatus according to claim 4, wherein thecircuitry is configured to transmit the frame including the informationdesignating the transmission waiting period such that a communicationapparatus whose number of times of transmission is smaller has a shortertransmission waiting period than a communication apparatus whose numberof times of transmission is larger.
 6. The access point apparatusaccording to claim 4, wherein the circuitry is configured to transmitthe frame including the information designating a shorter transmissionwaiting period for a communication apparatus which performs dataretransmission than a transmission waiting period of anothercommunication apparatus.
 7. The access point apparatus according toclaim 1, wherein, in the frame in which a category with higher priorityis designated, the information designating a transmission waiting periodshorter than a remaining period of a transmission waiting period set ina case where a category with lower priority is designated, is included.8. A communication method executed in an access point apparatuscomprising: transmitting a frame in which information of a categoryfavorable for uplink multi user transmission and information regarding atransmission waiting period of a communication apparatus after theuplink multi user transmission is finished are included; including, inthe frame, the information regarding the transmission waiting period ofthe communication apparatus in accordance with the category, thetransmission waiting period being longer than another transmissionwaiting period in a case where the access point apparatus performsanother uplink multi user transmission after the uplink multi usertransmission is finished; acquiring, based on back off, an opportunityto trigger the uplink multi user transmission; and acquiring, based onthe other transmission waiting period, another opportunity to triggerthe other uplink multi user transmission, wherein the category includesAC_VO, AC_VI, AC_BE, or AC_BK.
 9. A communication apparatus comprising:circuitry configured to set, on a basis of information regarding atransmission waiting period of the communication apparatus included in aframe received from an access point apparatus, a transmission waitingperiod after uplink multi user transmission is finished, the frameincluding information of a category favorable for the uplink multi usertransmission and the information regarding the transmission waitingperiod of the communication apparatus in accordance with the category,perform the uplink multi user transmission triggered by the access pointapparatus based on back off, perform, in a case where another uplinkmulti user transmission is triggered by the access point apparatus basedon another transmission waiting period, the other uplink multi usertransmission, and perform, in a case where the other uplink multi usertransmission is not triggered by the access point apparatus, uplinksingle user transmission based on the transmission waiting period,wherein the category includes AC_VO, AC_VI, AC_BE, or AC_BK, and whereinthe transmission waiting period is longer than the other transmissionwaiting period in a case where the other uplink multi user transmissionis performed after the uplink multiuser transmission is finished.
 10. Acommunication method executed in a communication apparatus comprising:setting, on a basis of information regarding a transmission waitingperiod of the communication apparatus included in a frame received froman access point apparatus, a transmission waiting period after uplinkmulti user transmission is finished, the frame including information ofa category favorable for the uplink multi user transmission and theinformation regarding the transmission waiting period of thecommunication apparatus in accordance with the category, performing theuplink multi user transmission triggered by the access point apparatusbased on back off, performing, in a case where another uplink multi usertransmission is triggered by the access point apparatus based on anothertransmission waiting period, the other uplink multi user transmission,and performing, in a case where the other uplink multi user transmissionis not triggered by the access point apparatus, uplink single usertransmission based on the transmission waiting period, wherein thecategory includes AC_VO, AC_VI, AC_BE, or AC_BK, and wherein thetransmission waiting period is longer than the other transmissionwaiting period in a case where the other uplink multi user transmissionis performed after the uplink multiuser transmission is finished.